1. Field of the Invention
The present invention relates generally to an infrared absorbent green glass composition that is excellent in infrared absorptivity and has a high visible light transmittance, and to laminated glass including the same.
2. Related Background Art
Many of the glass sheets to be used for vehicles and buildings are manufactured by a float process. The base glass composition thereof is so called soda-lime-silica glass. Usually, these glass sheets are installed in the windows of vehicles or buildings. From a viewpoint of energy saving, there is demand for the infrared absorbent glass sheets that have excellent infrared absorptivity. With respect to the glass sheets that are used for vehicles such as automobiles, depending on the special locations where they are to be disposed, the lower limit of visible light transmittance has been specified to ensure visibility and therefore an infrared absorbent glass sheet that has a high visible light transmittance is desired. For example, in Japan, the visible light transmittance of windshield glass of automobiles is specified to be at least 70%.
In order to improve the infrared absorptivity of soda-lime-silica glass, many techniques of utilizing the absorption by divalent iron (FeO) have been proposed (see, for instance, JP1(1989)-18938A (Reference 1), JP3(1991)-187946A (Reference 2), etc.). The iron oxides that are contained in a glass composition include FeO, which corresponds to divalent iron. The FeO intensively absorbs lights with wavelengths in the range of 550 to 1600 nm. Accordingly, when FeO is present, a glass composition can be obtained that has improved infrared absorptivity. Generally, the peak of the infrared absorption by FeO is about 1050 nm.
Reference 1 discloses, as Composition No. 4 in Table 1, a glass composition having the following composition and transmittance: COMPOSITION: expressed in mass %, SiO2 71.56%, Na2O 14.19%, K2O 0.05%, CaO 12.85%, MgO 0.16%, Al2O3 0.25%, SO3 0.17%, total iron expressed as Fe2O3 0.606%, FeO expressed as Fe2O3 0.270%, and the ratio of FeO expressed as Fe2O3 to the total iron 0.446; and TRANSMITTANCE (at a thickness of 5 mm): light transmittance (LTA) 68.8%, total solar infrared transmittance (TSIR) 10.8%, total solar energy transmittance (TSET) 37.7%, and total solar ultraviolet transmittance (TSUV) 43.8%.
Reference 2 discloses infrared and ultraviolet absorbent soda-lime-silica glass that contains approximately 0.51 to 0.96 wt % of Fe2O3, approximately 0.15 to 0.33 wt % of FeO, and approximately 0.2 to 1.4 wt % of CeO2 as main components.
In order further to advance the energy saving such as, for example, reduction in electric energy that is required for air-conditioning etc., it is effective to reduce “the feeling of heat” that human beings sense on their skin due to the sunlight that passes through a glass sheet to enter a car or a room. The reduction of the feeling of heat can be achieved by increasing the absorption of lights with wavelengths of 1100 nm and longer. Generally, the absorption can be increased by increasing the content of FeO in a glass composition. However, simply increasing the content of FeO causes an increase in absorption in the visible light range at the same time. Accordingly, even if the feeling of heat can be reduced, the uses of the glass composition are limited.
Hence, attempts have been made to improve the infrared absorptivity of a glass composition by shifting the absorption range of FeO to the longer wavelength side without reducing visible light transmittance excessively.
For instance, JP4(1992)-187539A (Reference 3) discloses a glass composition that forms potash-lime-silica glass and thereby allows the absorption range of FeO contained therein to shift to the longer wavelength side. The potash-lime-silica glass, however, has a problem of high raw material cost.
JP60(1985)-215546A (Reference 4) discloses a glass composition that have infrared absorptivity improved by using BaO that can shift the absorption range of FeO to the longer wavelength side, with the visible light transmittance being kept high.
JP8(1996)-500811A (WO94/14716A1; Reference 5) discloses a glass composition containing Fe2O3 and FeO. Reference 5 describes that “the presence of K2O can increase the infrared absorption of glass under given conditions” and “alkaline-earth oxides have a decisive effect in obtaining the characteristics of the glass according to the present invention. As a fact, limiting the ratio of MgO to 2% or lower, preferably omitting it in the intended additive form in the glass of the present invention makes it possible to improve the infrared absorptivity”. In the glass composition disclosed in Reference 5, the content of CaO that is an alkaline-earth oxide is 10 wt % or less.
Apart from these glass compositions, the present applicants have disclosed an ultraviolet/infrared absorbent glass that contains 5 to 15 wt % CaO as well as iron oxide and CeO2 as colorants, in WO99/25660A1 (Reference 6). Reference 6 describes that “CaO improves the durability of glass and is used for adjusting the viscosity and devitrification temperature in the glass forming process” and “it is necessary that total iron oxide (T—Fe2O3) expressed as Fe2O3 is 0.35 to 0.55%, FeO is 0.08 to 0.15%, and the ratio of FeO (expressed as Fe2O3)/T—Fe2O3 is in the range of at least 0.20 but lower than 0.27”.
Furthermore, the present applicants also have disclosed a glass composition that contains 5 to 15 wt % CaO as well as iron oxide and CeO2 as colorants, in JP2003-119048A (Reference 7). Reference 7 describes that “when the glass composition of the present invention has both higher visible light transmittance and lower infrared transmittance, it is preferable that it contain 0.4 to 1% of T—Fe2O3 and 0.01 to 0.40% of TiO2. This makes it possible to obtain glass with a visible light transmittance of at least 70% that is measured using the illuminant A, with the glass thickness being 1 to 6 mm” (Paragraph No. 0043).
On the other hand, JP8(1996)-259279A (Reference 8) discloses a technique of securing thermal insulation and transparency of laminated glass not by controlling the glass composition but instead by dispersing functional fine particles such as ITO (indium-tin oxide) in an interlayer film of the laminated glass. For instance, the laminated glass described in Example 3 of Reference 8 has a configuration in which ITO fine particles with diameters of 0.1 μm or smaller are dispersed in an interlayer thereof, and has a visible light transmittance TV of 76.3% and a solar radiation transmittance TS of 51.5%. However, since the functional fine particles of, for instance, ITO are expensive, the cost for manufacturing the laminated glass disclosed in Reference 8 is high. In addition, it is difficult to apply the technique disclosed in Reference 8 to a single glass sheet.